$de + 9df + 3d + 8 = -3e - 9$ Solve for $d$.
Solution: Combine constant terms on the right. $de + 9df + 3d + {8} = -3e - {9}$ $de + 9df + 3d = -3e - {17}$ Notice that all the terms on the left-hand side of the equation have $d$ in them. $1{d}e + 9{d}f + 3{d} = -3e - 17$ Factor out the $d$ ${d} \cdot \left( e + 9f + 3 \right) = -3e - 17$ Isolate the $d$ $d \cdot \left( {e + 9f + 3} \right) = -3e - 17$ $d = \dfrac{ -3e - 17 }{ {e + 9f + 3} }$